Molecular and genetic tools have been utilized that shed light on the genes that contribute to the susceptibility to murine lupus and the cellular and subcellular mechanisms that lead to immunopathology. The MHC genes and their products are amongst those that have been consistently shown to contribute towards development of disease. To understand the contribution of MHC genes, notably MHC class II, our laboratory has developed two new inbred strains, NZB.H-2b mice, like NZB.H-2d mice. The study of 10th generation animals is striding because NZB.H-2bm12 mice develop autoantibodies to dsDNA. In contrast, NZB.H-2b mice, like NZB.H-2d mice, develop low titer antibodies to ssDNA but have no evidence for production of antibodies to dsDNA. Furthermore, NZB.H-2bm12 mice manifest and IgM to IgG switch in the production of antibodies to dsDNA, demonstrate proteinuria, have reduced survival and glomerulonephritis at autopsy. Thus, the gene conversion at amino acid glomerulonephritis at autopsy. Thus, the gene conversion at amino acid residues 68, 71 and 72 of I-Ebetab that resulted in the I-Abm12 mutation has led to accelerated autoimmunity on the NZB background. this data is particularly interesting because the contribution of NZW to accelerated autoimmunity in the NZB x NZW Fl hybrid has recently been mapped to a single amino acid change at residue 72 of I- Ebeta. We believe that amino acid 72 is a hotspot for disorders of immune regulation. The use of our newly developed congenic NZB line expressing the I-Abm12 mutation will allow us to address the role of thymic education for anti-dsDNA responses and to determine whether abnormal autoantibodies to dsDNA are due to a selective defect at the T cell level or due to global abnormalities of B cells and/or macrophages. Similarly, we will be able to determine whether the induction of anti-dsDNA responses are MHC restricted and/or a result of abnormalities in the cytokine network. Finally, we will develop innovative techniques to clone T cells specific for dsDNA, permitting the study of T cell repertoire. We believe that NZB.H-2bm12 mice will allow specific dissection of the cellular requirements for autoantibody production uncomplicated by the issue of heterozygosity.